The invention is directed to a paper making wire or screen in the form of a composite fabric, comprising an upper or forming fabric and a lower or wear fabric consisting of at least three sets of longitudinal threads or strands and at least two sets of cross threads or strands.
Until now, prior known paper making wires or screen in the form of composite fabrics could not be successfully used for making fine papers due to the imperfect nature of the upper surface facing the paper, which resulted in all kinds of markings in the paper. In this connection longitudinal, cross and diagonal markings have been known which were so severe that in most cases the wires had to be eliminated from the paper making machine.
A forming wire or screen for paper making machines is known which consists of a first set of warp threads and a first set of weft threads, woven to form a first complete fabric, and further consists of a second set of warp threads and a second set of weft threads woven to form a second complete fabric. The first and second fabrics are bound together by means of special binding weft threads disposed between the fabrics, the binding weft threads being tied up with threads from the first and second sets of warp threads. However, with this known screen, the intended object, viz. to have the binding weft threads extend rather straight in the fabric body, wherein they are wrapped by warp threads of the upper and the lower fabric so that the binding points should be within the fabric body and not at the outer threads thereof in order not to affect the flatness of the paper-facing side, has not been achieved. The binding weft threads do not extend linearly but are severely bent and form regularly disposed duplicate knuckles with the weft threads of the upper fabric on the paper-facing side of the wire; these duplicate knuckles form depressions in the upper surface which even include adjacent knuckles. Consequently, the above-mentioned drawbacks, i.e. severe markings which are unacceptable for many paper grades and especially for fine papers, are not eliminated.
It is also known in the art to provide a forming wire or screen comprising a fine-mesh side facing the paper web and a wide-mesh side acting as wear side, the wire or screen being in the form of complete fabrics bound together with special binding warp threads; however, in this known structure no information is given in respect of the distribution of the binding points and the influence thereof on the paper-facing side of the wire or screen; one must assume therefore, that with this known wire or screen the undulating extension of the warp threads on the paper-facing side will also result in the mentioned disadvantageous markings.